This research project has two overall goals: (a) the validation of a new personal level approach to assessing potential inhaled dose of particulate air pollution; and (b) the assessment of this method to an important topic in air pollution epidemiology, namely the acute cardiovascular impacts of short term exposures while exercising in close proximity to air pollution sources. In this project we will focus on biking as the form of exercise, which brings many benefits ? increased exercise, less roadway congestion and reduced greenhouse gas emissions ? but it may cause increased exposures and doses to air pollution for those who choose biking over other transport modes. Reliable exposure assessment is the sine qua non of air pollution epidemiology, but studies have historically made do with imperfect proxies based on central site data, even though ambient concentrations are poor predictors of personal exposure. Personal exposure studies are seen as the gold standard to date but have had two major limitations- (a) they don?t take into account variations in volumetric respiration rates, and (b) personal studies are overly burdensome to do on a large scale. This proposal will work focus overcoming the first limitation and on minimizing the second. We will carry out cost-benefit analyses to put some quantitative estimates on how the improved metrics and protocols can reduce the needed size and cost of studies. The actual inhaled dose of an airborne pollutant is driven by the temporal overlap of high respiration rates and peak exposures, and thus of physical activity patterns and source proximity. The primary device that we propose to validate and deploy in the current study is the RTI MicroPEM? primarily developed with early Gene Environment Initiative funding. We will use the MicroPEM?s onboard accelerometer to estimate the minute ventilation rate (the volume of air inhaled per minute) and combine this information with minute-by-minute air pollution concentrations to calculate potential inhaled dose (in micrograms/minute). The validation phase of the project will focus on improving methods for predicting minute ventilation from accelerometer data and validating PM2.5 measurements, with pretesting in lab and field settings. The second phase of the project will entail deploying MicroPEMs in a cohort of urban cyclists, who will also be outfitted with devices to measure black carbon exposures, ambulatory blood pressure and heart rate variability. Using day-to-day variation in exposures during the morning commute, we will estimate the association between short-term air pollution exposures and acute cardiovascular parameters. The proposed work builds on a partnership between Columbia University and WNYC, the nation?s largest public radio station and involves a team comprising Columbia environmental health scientists, cardiologists, and exposure assessment experts, and core members of the RTI team that developed the MicroPEM device.